Slaprunner SR: add erp5.util for resiliency test.

Also add slapos.cookbook to the list of eggs;
slaprunner recipe: remove trailing / from master_url.

Otherwise, it breaks slapproxy.
(Even if slapproxy should support it, but that's another story.)
helloworld SR: redirect output to log.

Also improve overall quality.
Slaprunner SR: resiliency: don't hardcode parameters to send.

It is done automatically through the resilient stack.
Slaprunner SR: Set resiliency-backup-periodicity parameter so that periodicity is done every 5 minutes.
librecipe: add pidfile option for singletons.
Resiliency: Use new pidfile option.
Slaprunner SR: allow to specify custom domain for frontends.
Slaprunner SR: resiliency test: Add dummy domain that we don't own so that promises pass.
TEMP: Use good branch for development.